Based on the theory of Fluid Dynamics CFD and Fluid analysis software Fluent，we accomplished the flow field simulation of internal speed and internal pressure of pneumatic oil mist atomizer. Both the flow field simulation and the results of experiment are in good agreement，particle size and density of oil mist change very little when the pressure of compressed air is kept constant while the distance of nozzle and baffle is varied. When the distance from nozzle to baffle is fixed, and the pressure of compressed air is increased gradually, the density of oil mist will increase and the particle size of oil mist will decrease along with the increasing pressure of compressed air. This decreasing trend of particle size of oil mist will slow down when the pressure of compressed air increases to 0.35Mpa. The particle size of oil mist can reach 2μm.